1. Field of the Invention
This invention relates generally to a method and apparatus for selectively feeding sheets of paper to a printer, a copier, or the like, and, more particularly, to a method and apparatus for selectively engaging multiple stacks of paper and feeding single sheets from the selected stack of paper to a printer, a copier, or the like.
2. Description of the Related Art
In the field of printers, paper handling mechanisms typically employ a separate sheet feeding mechanism for each tray of paper that the printer has the ability to access. Each pair of trays and sheet feeding mechanisms are normally stacked in a vertical arrangement and consume vertical space equal to the height of each tray and the height of each sheet feeding mechanism. Accordingly, the vertical height of each tray and sheet feeding mechanism limits the maximum number of trays that can be associated with a paper handling mechanism if a printer is to be used in a desktop environment.
In eleotrophotographic printers, such as desktop laser printers, these trays typically are configured to hold approximately 250 sheets of paper. The trays include a bottom portion that supports the stack of paper. The bottom portion is hinged, and a spring acts against the bottom portion to pivot the bottom portion upwardly. Thus, the stack of paper pivots upwardly against the stationary sheet feeding mechanism associated with that tray.
Since the spring force constantly maintains the paper in contact with the sheet feeding mechanism, paper cannot be added to the tray unless the tray is removed. Thus, the printing process from that tray must cease while the tray is removed to replenish the paper supply. In addition, the printing process from that tray must cease when the user wishes to print a short run of unique paper that differs from the paper currently in the tray.
To overcome this inherent deficiency, previous laser printers have employed a sheet feeding mechanism that allows a user to singularly and consecutively feed a small number of sheets into the printer. Of course, this process does not free the user to accomplish other tasks, but requires that the user remain at the printer, consecutively feeding each sheet of paper until the entire printing process is completed. Alternatively, the user may remove the tray from the paper handling mechanism insert the desired number of sheets of paper into the tray and replace the tray into the paper handling mechanism. While this method does free the user to leave the printer during the printing process, the procedure of removing and loading the tray slows the printing process.
Another problem arises due to a pressure variation between the sheet feeding mechanism and the stack of paper. The pressure varies with the thickness of the stack of paper remaining in the tray, because the force applied by the spring is dependent upon the degree of compression of the spring, which is nonlinear. This pressure variation can cause the sheet feeding mechanism to occasionally misfeed a sheet of paper.
Typically, laser printers insure that a single sheet is selected from the stack of paper in the tray by employing a "corner buckler." A corner buckler is a small tab of metal that is placed in one corner of each tray. The sheet feeding mechanism contacts the top sheet of paper in the tray, and moves the sheet toward the corner buckler. As the sheet leaves the tray, the corner buckler deforms the corner of the top sheet of paper to separate it from any lower sheets. However, if two sheets of paper are stuck together and moving out of the tray, occasionally the deformation produced by the corner buckler will not be sufficient to separate these sheets from one another. Moreover, the corner buckler limits the speed at which paper may be removed from the tray.
Since the market for desktop printers is highly competitive extremely cost sensitive, any proposed solution to these problems, or other advances in printer technology, should be economical, durable, and easy to manufacture and repair.
The present invention is directed to overcoming, or at least minimizing, one or more of the problems as set forth above.